The present invention relates to an ultrasonic control device and, more specifically, to a microprocessor controlled ultrasonic generator for use with a magnetostrictive element, which automatically adjusts to the resonant mechanical frequency of a tip-insert combination of a dental scaler or the like, thereby allowing the user to substitute or replace tips as desired. Upon startup or reset, the controller automatically steps through a range of frequencies, storing the resonant frequency for the tip system. The controller thereafter maintains the tip system in use at or near the resonant frequency of the tip providing the most efficient use of the device.
1. Prior Art
Warrin, in U.S. Pat. No. 4,820,152, teaches the use of a multi-purpose handpiece which is capable of sensing the type of tip insert being utilized and adjust or tune the circuitry accordingly.
Hetzel, in U.S. Pat. No. 5,059,122, teaches the use of tuning the frequency of an oscillator to match the feedback from the response of the mechanical resonant frequency of the dental insert.
Sharp, in U.S. Pat. No. 5,730,594, teaches an ultrasonic dental scaler which is driven by a switch selectable circuit to either automatically tune to the resonant frequency or to permit manual adjustment of the frequency of the oscillator. Sharp, in U.S. Pat. No. 5,451,161 teaches automatically tuning an oscillating circuit to match the resonant frequency of the tip insert.
2. Background
Ultrasonic medical devices, such as dental scalers, driven by coils surrounding magnetostrictive elements, are well known in the art. In such ultrasonic devices, vibrational motion results from an oscillating current being supplied to the coil which induces a magnetostrictive element to begin oscillating. The oscillation of the magnetostrictive element translates into flexural or elliptical motion of an insert tip. The magnetostrictive element is affixed at a node to an element, generally described as a velocity transducer, which translates the vibration to the distal tip of the insert system. In dental hygiene applications, the tip contacts accumulated calculus on the tooth surface to dislodge the calculus. The tip also provides a pathway for irrigating the area where the tip is used by dispensing a liquid, most often water, through or over the surface of the tip. The flow of liquid through the hand piece also dissipates heat generated by Joule heating of the coil/magnetostrictive element.
Ultrasonic scalpels may also be driven by the vibration caused by an energized coil around a stack of magnetostrictive plates, such as nickel or nickel alloy, which transmits its vibratory motion through an intermediate element, called a velocity transducer, to a cutting tip. Some prior art devices controlled current levels to the energizing coil of the magnetostrictive element by placing secondary pickup coils to measure power transfer. The present invention does not require any secondary coils to control the vibration of the tip. Some prior art devices devised numerous methods of determine the type of tip system in use. The present invention automatically adapts to the natural acoustic frequency of the tip system being used permitting a wide variety of frequency response to a variety of tip systems.
Other prior art devices allowed only a switch-selectable frequency choice. In the present invention, the frequency tunes automatically from the feedback received from the magnetostrictive tip system in operation.
Some other prior art dental scaler devices automatically sought a higher resonant frequency within the designed bandwidth around one or two design frequencies. The automatic tuning feature of these prior art devices provided unstable tip operation because these circuits were constantly changing frequency during the procedure, providing an uncomfortable experience for the patient. In the present invention, the resonant frequency is locked into the control circuit to provide smooth operation.
The present invention provides a microprocessor to automatically sense the appropriate mechanical resonant frequency by its effect on the power consumption of the power supply, lock on to that frequency, optionally allowing the user to offset from the resonant frequency and variably adjust the amplitude of the tip system with minimal user intervention. Heretofore, so far as known to applicant, the design of the magnetostrictive devices was limited to the frequency of the driving circuitry. The physical characteristics of the magnetostrictive stack, velocity transducer and tip defined the resonant frequency of the system that was required to be matched to the oscillating frequency of the coil. The present invention reduces, if not eliminates, this problem. In operation, the technician would insert the tip into the hand piece, reset the microprocessor (alternatively, for example, from the front panel, the foot switch, a handpiece switch, a voice command, or upon the passage of a preset time interval measured by the microprocessor), the microprocessor would then sweep or step through a range of frequencies preset in the memory of the microprocessor and selectively tune the system to its maximum or resonant acoustic frequency. The front panel of the system would provide means for selectively setting an offside frequency (from the resonant frequency) thereby increasing the comfort of the patient or reducing the vibration of the tip. The appropriate resonant acoustic frequency would be determined upon boot or reset of the microprocessor and would not thereafter be changed unless the operator desired to change the setting or a new tip system was installed in the hand piece. This feature would allow technicians to choose the appropriate tip system to achieve the maximum efficiency and comfort in the dental scaling, polishing or surgical process.
The present invention allows the user to control, for example, a dental scaler tip system, an ultrasonic polisher, a surgical scalpel, or a feline urinary tract probe (each having a significantly different resonant acoustic frequency profiles) on the handpiece and the controller will adjust automatically to the most efficient resonant frequency. This invention allows a large variation of driven elements (for example, tips, polishing stones, surgical blades, etc.), greatly increasing the functionality of ultrasonic usage. Other uses of the ultrasonic controller capable of automatically adapting to a broad spectrum of resonant frequencies may be suggested.
For example, in the feline urinary tract probe, a long thin hollow probe was attached to the end of a low frequency (and low power) magnetostrictive stack to break up and flush away urine crystals in male cat""s urinary tracts. The probe is not easily controlled on a standard ultrasonic generator at 25 or 30 kHz. The present system would automatically compensate for the natural acoustical resonance of the tip system and determine the appropriate setting, while providing a very smooth and controllable ultrasonic activity, despite the possibility of different probe lengths and shapes.